ENME382 S2010 0201 ch06

ENME382 S2010 0201 ch06 - Chapter 6: Diffusion ISSUES TO...

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ISSUES TO ADDRESS. .. How does diffusion occur? Chapter 6: Diffusion Chapter 6 - ENME 382 Spring 2010 Section 0201 1 Why is it an important part of processing? How can the rate of diffusion be predicted for some simple cases? How does diffusion depend on structure and temperature?
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Diffusion Diffusion - Mass transport by atomic motion Mechanisms ases & Liquids ndom (Brownian) motion Chapter 6 - ENME 382 Spring 2010 Section 0201 2 • Solids – vacancy diffusion or interstitial diffusion
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Interdiffusion : In an alloy, atoms tend to migrate from regions of high conc. to regions of low conc. Initially Adapted from Figs. 6.1 and 6.2, Callister & Diffusion After some time Chapter 6 - ENME 382 Spring 2010 Section 0201 3 Rethwisch 3e .
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Self-diffusion : In an elemental solid, atoms also migrate. Label some atoms Diffusion A C After some time C D Chapter 6 - ENME 382 Spring 2010 Section 0201 4 B D A B
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Diffusion Mechanisms Vacancy Diffusion: atoms exchange with vacancies applies to substitutional impurities atoms rate depends on: -- number of vacancies -- activation energy to exchange. Chapter 6 - ENME 382 Spring 2010 Section 0201 5 increasing elapsed time
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• Simulation of interdiffusion across an interface: Rate of substitutional iffusion depends on: Diffusion Simulation QuickTime™ and a Cinepak decompressor are needed to see this picture. Chapter 6 - ENME 382 Spring 2010 Section 0201 6 diffusion depends on: -- vacancy concentration -- frequency of jumping. (Courtesy P.M. Anderson)
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Diffusion Mechanisms • Interstitial diffusion – smaller atoms can diffuse between atoms. Chapter 6 - ENME 382 Spring 2010 Section 0201 7 More rapid than vacancy diffusion Adapted from Fig. 6.3 (b), .
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chapter-opening photograph, Chapter 6, Callister & Rethwisch 3e. (Courtesy of Surface Division, Midland-Ross.) Case Hardening : -- Diffuse carbon atoms into the host iron atoms at the surface. -- Example of interstitial diffusion is a case ardened gear. Processing Using Diffusion
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ENME382 S2010 0201 ch06 - Chapter 6: Diffusion ISSUES TO...

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